1. Field of the Invention
The present invention generally relates to cased telescoped ammunition and, more particularly, is concerned with features for augmenting retention and retraction of cartridge case end caps of the ammunition round.
2. Description of the Prior Art
Cased telescoped ammunition is generally well-known. Representative prior art versions of such ammunition are disclosed in U.S. patents to Meyer et al (U.S. Pat. No. 2,866,412), Kunz (U.S. Pat. No. 2,996,988), LaFever et al (U.S. Pat. No. 4,197,801), Smith (U.S. Pat. No. 4,220,089), Bains (U.S. Pat. No. 4,335,657) and Clarke et al (U.S. Pat. No. 4,604,954).
Typically, a round of cased telescoped ammunition includes an elongated cylindrical case defining a chamber that contains a propellant charge. The propellant charge has an axial bore through which extends a central tube in coaxial relation with the case and fastened at its opposite ends to the opposite ends of the case. A telescoped projectile is housed within a forward portion of the central tube, whereas an aft portion of the central tube, referred to as a control section, receives a piston or spud on the aft end of the projectile. A primer is positioned within the control section aft of the projectile spud, and a small amount of propellant is contained therein between the primer and the spud.
The round of ammunition is loaded in a gun chamber located rearwardly of the gun barrel. When the round is fired, the primer ignites the small amount of propellant in the control section. The resulting gas applies a force against the spud, driving the projectile forwardly out of the central tube and into the gun barrel. Next, the hot gas ignites the main propellant charge surrounding the projectile. Burning of the propellant charge produces gas at much higher pressure which drives the projectile through the gun barrel to exit the muzzle at high velocity.
The increasing pressure created by the burning propellant charge expands the ammunition case axially and radially. The pressure also acts to elastically deform the gun, enlarging the chamber.
Then, when the pressure is relieved by exit of the projectile from the gun barrel, the gun chamber reverts to its unpressurized dimensions. In order to extract the case from the gun chamber, it is necessary that the case return or recover at least to dimensions which allow clearance between it and the ends and interior surface of the chamber.
It is seen, therefore, that the ammunition cartridge case must expand axially and radially during firing to accommodate the structural response of the gun chamber to gun gas pressure. Such cartridge cases are fitted with end caps which seal the chamber to prevent escape of high pressure gun gas. In addition to sealing the chamber during firing, the end caps must be retained by the cylindrical skin tube of the case and must not retard the axial shrinkage of the gun chamber after firing. Retardation would slow the gun and separation of an end cap from the first case of the ammunition round could cause a gun stoppage.
Therefore, it is essential that features be incorporated in the ammunition round which will ensure that effective end cap retention and retraction take place.